Cyclodepsipeptides from marine sponges: natural agents for drug research

Total Syntheses of Colletopeptide A and Colletotrichamide A

The first total syntheses of cyclic depsipeptides colletopeptide A and colletotrichamide A, have been accomplished. The key advanced intermediate, a cyclic tridepsipeptide derivative, was constructed using a sequence of transformations that features asymmetric Brown crotylation, cross metathesis, Yamaguchi esterification, ozonolysis, and macrolactamization. A late-stage incorporation of the mannose fragment completed the synthesis of colletotrichamide A, and the desilylation of the common intermediate gave rise to colletopeptide A, which led to unambiguous confirmation of the absolute stereochemistry of the aforementioned natural products.

Absolute Stereochemistry Determination of Bioactive Marine-Derived Cyclopeptides by Liquid Chromatography Methods: An Update Review (2018-2022)

Cyclopeptides are considered as one of the most important classes of compounds derived from marine sources, due to their structural diversity and a myriad of their biological and pharmacological activities. Since marine-derived cyclopeptides consist of different amino acids, many of which are non-proteinogenic, they possess various stereogenic centers. In this respect, the structure elucidation of new molecular scaffolds obtained from natural sources, including marine-derived cyclopeptides, can become a very challenging task. The determination of the absolute configurations of the amino acid residues is accomplished, in most cases, by performing acidic hydrolysis, followed by analyses by liquid chromatography (LC). In a continuation with the authors' previous publication, and to analyze the current trends, the present review covers recently published works (from January 2018 to November 2022) regarding new cyclopeptides from marine organisms, with a special focus on their biological/pharmacological activities and the absolute stereochemical assignment of the amino acid residues. Ninety-one unreported marine-derived cyclopeptides were identified during this period, most of which displayed anticancer or antimicrobial activities. Marfey's method, which involves LC, was found to be the most frequently used for this purpose.

Solonamides, a Group of Cyclodepsipeptides, Influence Motility in the Native Producer Photobacterium galatheae S2753

The marine bacterium Photobacterium galatheae S2753 produces a group of cyclodepsipeptides, called solonamides, which impede the virulence but not the survival of Staphylococcus aureus. In addition to their invaluable antivirulence activity, little is known about the biosynthesis and physiological function of solonamides in the native producer. This study generated a solonamide-deficient (Δsol) mutant by in-frame deletion of the sol gene, thereby identifying the core gene for solonamide biosynthesis. By annotation from antiSMASH, the biosynthetic pathway of solonamides in S2753 was also proposed. Mass spectrometry analysis of cell extracts found that deficiency of solonamide production influenced the production of a group of unknown compounds but otherwise did not alter the overall secondary metabolite profile. Physiological comparison between Δsol and wild-type S2753 demonstrated that growth dynamics and biofilm formation of both strains were similar; however, the Δsol mutant displayed reduced motility rings compared to the wild type. Reintroduction of sol restored solonamide production and motility to the mutant, indicating that solonamides influence the motility behavior of P. galatheae S2753. Proteomic analysis of the Δsol and wild-type strains found that eliminating solonamides influenced many cellular processes, including swimming-related proteins and proteins adjusting the cellular cyclic di-GMP concentration. In conclusion, our results revealed the biosynthetic pathway of solonamides and their ecological benefits to P. galatheae S2753 by enhancing motility, likely by altering the motile physiology. IMPORTANCE The broad range of bioactive potentials of cyclodepsipeptides makes these compounds invaluable in the pharmaceutical industry. Recently, a few novel cyclodepsipeptides have been discovered in marine Proteobacteria; however, their biosynthetic pathways remain to be revealed. Here, we demonstrated the biosynthetic genetic basis and pathway of the antivirulence compounds known as solonamides in P. galatheae S2753. This can pave the way for the biological overproduction of solonamides on an industrial scale. Moreover, the comparison of a solonamide-deficient mutant and wild-type S2753 demonstrated that solonamides stimulate the swimming behavior of S2753 and also influence a few key physiological processes of the native producers. These results evidenced that, in addition to their importance as novel drug candidates, these compounds play a pivotal role in the physiology of the producing microorganisms and potentially provide the native producer competitive benefits for their survival in nature.

Therapeutic Potential of Marine Bioactive Peptides against Human Immunodeficiency Virus: Recent Evidence, Challenges, and Future Trends

Acquired immunodeficiency syndrome (AIDS) is a chronic and potentially fatal ailment caused by the human immunodeficiency virus (HIV) and remains a major health problem worldwide. In recent years, the research focus has shifted to a greater emphasis on complementing treatment regimens involving conventional antiretroviral (ARV) drug therapies with novel lead structures isolated from various marine organisms that have the potential to be utilized as therapeutics for the management of HIV-AIDS. The present review summarizes the recent developments regarding bioactive peptides sourced from various marine organisms. This includes a discussion encompassing the potential of these novel marine bioactive peptides with regard to antiretroviral activities against HIV, preparation, purification, and processing techniques, in addition to insight into the future trends with an emphasis on the potential of exploration and evaluation of novel peptides to be developed into effective antiretroviral drugs.

The Immune System of Marine Organisms as Source for Drugs against Infectious Diseases

The high proliferation of microorganisms in aquatic environments has allowed their coevolution for billions of years with other living beings that also inhabit these niches. Among the different existing types of interaction, the eternal competition for supremacy between the susceptible species and their pathogens has selected, as part of the effector division of the immune system of the former ones, a vast and varied arsenal of efficient antimicrobial molecules, which is highly amplified by the broad biodiversity radiated, above any others, at the marine habitats. At present, the great recent scientific and technological advances already allow the massive discovery and exploitation of these defense compounds for therapeutic purposes against infectious diseases of our interest. Among them, antimicrobial peptides and antimicrobial metabolites stand out because of the wide dimensions of their structural diversities, mechanisms of action, and target pathogen ranges. This revision work contextualizes the research in this field and serves as a presentation and scope identification of the Special Issue from Marine Drugs journal “The Immune System of Marine Organisms as Source for Drugs against Infectious Diseases”.

Anti-inflammatory, anti-infectious and anti-cancer potential of marine algae and sponge: A review

Marine organisms are potentially a pretty good source of highly bioactive secondary metabolites that are best known for their anti-inflammation, anti-infection, and anti-cancer potential. The growing threat of bacterial resistance to synthetic antibiotics, is a potential source to screen terrestrial and marine natural organisms to discover promising anti-inflammatory and antimicrobial agents which can synergistically overcome the inflammatory and infectious disases. Algae and sponge have been studied enormously to evaluate their medicinal potential to fix variety of diseases, especially inflammation, infections, cancers, and diabetes. Cytarabine is the first isolated biomolecule from marine organism which was successfully practiced in clinical setup as chemotherapeutic agent against xylogenous leukemia both in acute and chronic conditions. This discovery opened the horizon for systematic evaluation of broad range of human disorders. This review is designed to look into the literature reported on anti-inflammatory, anti-infectious, and anti-cancerous potential of algae and sponge to refine the isolated compounds for value addition process.

Possible Functional Roles of Patellamides in the Ascidian-Prochloron Symbiosis

Patellamides are highly bioactive compounds found along with other cyanobactins in the symbiosis between didemnid ascidians and the enigmatic cyanobacterium Prochloron. The biosynthetic pathway of patellamide synthesis is well understood, the relevant operons have been identified in the Prochloron genome and genes involved in patellamide synthesis are among the most highly transcribed cyanobacterial genes in hospite. However, a more detailed study of the in vivo dynamics of patellamides and their function in the ascidian-Prochloron symbiosis is complicated by the fact that Prochloron remains uncultivated despite numerous attempts since its discovery in 1975. A major challenge is to account for the highly dynamic microenvironmental conditions experienced by Prochloron in hospite, where light-dark cycles drive rapid shifts between hyperoxia and anoxia as well as pH variations from pH ~6 to ~10. Recently, work on patellamide analogues has pointed out a range of different catalytic functions of patellamide that could prove essential for the ascidian-Prochloron symbiosis and could be modulated by the strong microenvironmental dynamics. Here, we review fundamental properties of patellamides and their occurrence and dynamics in vitro and in vivo. We discuss possible functions of patellamides in the ascidian-Prochloron symbiosis and identify important knowledge gaps and needs for further experimental studies.

Bioactive Peptides: Synthesis, Sources, Applications, and Proposed Mechanisms of Action

Bioactive peptides are a group of biological molecules that are normally buried in the structure of parent proteins and become active after the cleavage of the proteins. Another group of peptides is actively produced and found in many microorganisms and the body of organisms. Today, many groups of bioactive peptides have been marketed chemically or recombinantly. This article reviews the various production methods and sources of these important/ubiquitous and useful biomolecules. Their applications, such as antimicrobial, antihypertensive, antioxidant activities, blood-lipid-lowering effect, opioid role, antiobesity, ability to bind minerals, antidiabetic, and antiaging effects, will be explored. The types of pathways proposed for bioactive applications will be in the next part of the article, and at the end, the future perspectives of bioactive peptides will be reviewed. Reading this article is recommended for researchers interested in various fields of physiology, microbiology, biochemistry, and nanotechnology and food industry professionals.

Computational peptidology approach to the study of the chemical reactivity and bioactivity properties of Aspergillipeptide D, a cyclopentapeptide of marine origin

Aspergillipeptide D is a cyclic pentapeptide isolated from the marine gorgonian Melitodes squamata-derived fungus Aspergillus sp. SCSIO 41501 that it has been shown to present moderate activity against herpes virus simplex type 1 (HSV-1). Thus, this paper presents the results of a computational study of this cyclopentapeptide's chemical reactivity and bioactivity properties using a CDFT-based computational peptidology (CDFT-CP) methodology, which is derived from combining chemical reactivity descriptors derived from Conceptual Density Functional Theory (CDFT) and some Cheminformatics tools which may be used. This results in an improvement of the virtual screening procedure by a similarity search allowing the identification and validation of the known ability of the peptide to act as a possible useful drug. This was followed by an examination of the drug's bioactivity and pharmacokinetics indices in relation to the ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) characteristics. The findings provide further evidence of the MN12SX density functional's superiority in proving the Janak and Ionization Energy theorems using the proposed KID approach. This has proven to be beneficial in accurately predicting CDFT reactivity characteristics, which aid in the understanding of chemical reactivity. The Computational Pharmacokinetics study revealed the potential ability of Aspergillipeptide D as a therapeutic drug through the interaction with different target receptors. The ADMET indices confirm this assertion through the absence of toxicity and good absorption and distribution properties.

Can be marine bioactive peptides (MBAs) lead the future of foodomics for human health?

Marine organisms are considered a cache of biologically active metabolites with pharmaceutical, functional, and nutraceutical properties. Among these, marine bioactive peptides (MBAs) present in diverse marine species (fish, sponges, cyanobacteria, fungi, ascidians, seaweeds, & mollusks) have acquired attention owing to their broad-spectrum health-promoting benefits. Nowadays, scientists are keener exploring marine bioactive peptides precisely due to their unique structural and biological properties. These MBAs have reported ameliorating potential against different diseases like hypertension, diabetes, obesity, HIV, cancer, oxidation, and inflammation. Furthermore, MBAs isolated from various marine organisms may also have a beneficial role in the cosmetic, nutraceutical, and food industries. Few marine peptides and their derivative are approved for commercial use, while many MBAs are in various pre-clinical and clinical trials. This review mainly focuses on the diversity of marine bioactive peptides in marine organisms and their production procedures, such as chemical and enzymatic hydrolysis. Moreover, MBAs' therapeutic and biological potential has also been critically discussed herein, along with their status in drug discovery, pre-clinical and clinical trials.

Computational Pharmacokinetics Report, ADMET Study and Conceptual DFT-Based Estimation of the Chemical Reactivity Properties of Marine Cyclopeptides

Homophymines A-E and A1-E1 are bioactive natural cyclodepsipeptides with a complex molecular architecture. These molecules could have a potential use as antimicrobial, antiviral, and anticancer substances. We have carried out a computational study of the properties of this family of marine peptides using a CDFT-based Computational Peptidology (CDFT-CP) methodology that results from the combination of the chemical reactivity descriptors that arise from conceptual Density Functional Theory (CDFT) together with cheminformatics tools. The latter can be used to estimate the associated physicochemical parameters and to improve the process of virtual screening through a similarity search. Using this approach, the ability of the peptides to behave as a potentially useful drugs can be investigated. An analysis of their bioactivity and pharmacokinetics indices related to the ADMET (Absorption, Distribution, Metabolism, Excretion and Toxicity) features has also been carried out.

An integrated molecular modeling protocol for drug screening based on conceptual density functional theory and chemoinformatics for the study of marine cyclopeptides

An integrated molecular modeling protocol resulting from the combination of conceptual density functional theory (CDFT) chemical reactivity descriptors with several chemoinformatics tools has been used for the study of the chemical reactivity and bioactivity properties of a group of marine cyclic peptides. CP-CDFT is a branch of computational chemistry and molecular modeling dedicated to the study of peptides. The protocol allowed the estimation of the CDFT-based reactivity indices together with the associated physicochemical parameters that can help to identify the ability of the studied peptides to behave as potential useful drugs. This was complemented with an analysis of the bioactivity and pharmacokinetics parameters related to the ADMET (absorption, distribution, metabolism, excretion, and toxicity) features. Some examples related to the ability of the CDFT-based chemical reactivity descriptors for the prediction of the pKas of the peptides as well as their potential as AGE inhibitors are also presented.

A CDFT-Based Computational Peptidology (CDFT-CP) Study of the Chemical Reactivity and Bioactivity of the Marine-Derived Alternaramide Cyclopentadepsipeptide

Alternaramide is a cyclic pentadepsipeptide isolated from marine sources that has been shown to present weak antibiotic activity against Bacillus subtilis and Staphylococcus aureus as well as inhibitory effects on inflammatory mediator expressions. Thus, this work reports the results of a computational study of the chemical reactivity and bioactivity properties of this cyclopentadepsipeptide considering a CDFT-based computational peptidology (CDFT-CP) methodology that results from the combination of the chemical reactivity descriptors that arise from conceptual density functional theory (CDFT) together with some cheminformatics tools that can be used to estimate the associated physicochemical parameters, to improve the process of virtual screening through a similarity search, and to identify the ability of the peptide to behave as a potential useful drug, complemented with an analysis of its bioactivity and pharmacokinetics indices related to the ADMET (absorption, distribution, metabolism, excretion, and toxicity) features. The results represent a new confirmation of the superiority of the MN12SX density functional in the fulfilment of the Janak and ionization energy theorems through the proposed KID procedure. This has been useful for the accurate prediction of the CDFT reactivity descriptors that help in understanding the chemical reactivity. The computational pharmacokinetics study revealed the potential ability of alternaramide as a therapeutic drug by interacting with GPCR ligands and protease inhibitors. The ADMET indices confirm this assertion through the absence of toxicity and good absorption and distribution properties.

Evaluation of Microalgae Antiviral Activity and Their Bioactive Compounds

During the last year, science has been focusing on the research of antivirally active compounds overall after the SARS-CoV-2 pandemic, which caused a great amount of deaths and the downfall of the economy in 2020. Photosynthetic organisms such as microalgae are known to be a reservoir of bioactive secondary metabolites; this feature, coupled with the possibility of achieving very high biomass levels without excessive energetic expenses, make microalgae worthy of attention in the search for new molecules with antiviral effects. In this work, the antiviral effects of microalgae against some common human or animal viruses were considered, focusing our attention on some possible effects against SARS-CoV-2. We summed up the data from the literature on microalgae antiviral compounds, from the most common ones, such as lectins, polysaccharides and photosynthetic pigments, to the less known ones, such as unidentified proteins. We have discussed the effects of a microalgae-based genetic engineering approach against some viral diseases. We have illustrated the potential antiviral benefits of a diet enriched in microalgae.

Tavarua Deoxyriboside A and Jasplakinolide as Potential Neuroprotective Agents: Effects on Cellular Models of Oxidative Stress and Neuroinflammation

The oceans harbor a great reservoir of molecules with unknown bioactivities, which could be useful for the treatment of illnesses that nowadays have no cure, such as neurodegenerative diseases. In this work, we evaluated the neuroprotective potential of the marine Fijian compounds tavarua deoxyriboside A and jasplakinolide against oxidative stress and neuroinflammation, crucial mechanisms in neurodegeneration. Both metabolites protected SH-SY5Y human neuroblastoma cells from H₂O₂ damage, improving mitochondrial function and activating the antioxidant systems of cells. These effects were mediated by their ability of inducing Nrf2 translocation. In BV2 microglial cells activated with lipopolysaccharide, Fijian metabolites also displayed promising results, decreasing the release of proinflammatory mediators (ROS, NO, cytokines) through the reduction of gp91 and NFkB-p65 expression. Finally, we performed a coculture among both cell lines, in which treatment with compounds protected SH-SY5Y cells from activated microglia, corroborating their neuroprotective effects. These results suggest that tavarua deoxyriboside A and jasplakinolide could be used as candidate molecules for further studies against neurodegeneration.

Connecting the conformational behavior of cyclic octadepsipeptides with their ionophoric property and membrane permeability

Cyclic octadepsipeptides such as PF1022A and its synthetic derivative emodepside exhibit anthelmintic activity with the latter sold as a commercial drug treatment against gastrointestinal nematodes for animal health use. The structure-permeability relationship of these cyclic depsipeptides that could ultimately provide insights into the compound bioavailability is not yet well understood. The fully N-methylated amide backbone and apolar sidechain residues do not allow for the formation of intramolecular hydrogen bonds, normally observed in the membrane-permeable conformations of cyclic peptides. Hence, any understanding gained on these depsipeptides would serve as a prototype for future design strategies. In previous nuclear magnetic resonance (NMR) studies, two macrocyclic core conformers of emodepside were detected, one with all backbone amides in trans-configuration (hereon referred as the symmetric conformer) and the other with one amide in cis-configuration (hereon referred as the asymmetric conformer). In addition, these depsipeptides were also reported to be ionophores with a preference of potassium over sodium. In this study, we relate the conformational behavior of PF1022A, emodepside, and closely related analogs with their ionophoric characteristic probed using NMR and molecular dynamics (MD) simulations and finally evaluated their passive membrane permeability using PAMPA. We find that the equilibrium between the two core conformers shifts more towards the symmetric conformer upon addition of monovalent cations with selectivity for potassium over sodium. Both the NMR experiments and the theoretical Markov state models based on extensive MD simulations indicate a more rigid backbone for the asymmetric conformation, whereas the symmetric conformation shows greater flexibility. The experimental results further advocate for the symmetric conformation binding the cation. The PAMPA results suggest that the investigated depsipeptides are retained in the membrane, which may be advantageous for the likely target, a membrane-bound potassium channel.

Virtual Screening of Marine Natural Compounds by Means of Chemoinformatics and CDFT-Based Computational Peptidology

This work presents the results of a computational study of the chemical reactivity and bioactivity properties of the members of the theopapuamides A-D family of marine peptides by making use of our proposed methodology named Computational Peptidology (CP) that has been successfully considered in previous studies of this kind of molecular system. CP allows for the determination of the global and local descriptors that come from Conceptual Density Functional Theory (CDFT) that can give an idea about the chemical reactivity properties of the marine natural products under study, which are expected to be related to their bioactivity. At the same time, the validity of the procedure based on the adoption of the KID (Koopmans In DFT) technique, as well as the MN12SX/Def2TZVP/H2O model chemistry is successfully verified. Together with several chemoinformatic tools that can be used to improve the process of virtual screening, some additional properties of these marine peptides are identified related to their ability to behave as useful drugs. With the further objective of analyzing their bioactivity, some useful parameters for future QSAR studies, their predicted biological targets, and the ADMET (Absorption, Distribution, Metabolism, Excretion and Toxicity) parameters related to the theopapuamides A-D pharmacokinetics are also reported.

Bioactive compounds from marine invertebrates as potent anticancer drugs: the possible pharmacophores modulating cell death pathways

Marine invertebrates are extremely diverse, largely productive, untapped oceanic resources with chemically unique bioactive lead compound contributing a wide range of screening for the discovery of anticancer compounds. The lead compounds have unfurled an extensive array of pharmacological properties owing to the presence of polyphenols, alkaloids, terpenoids and other secondary metabolites. The antioxidant, immunomodulatory and anti-tumor activities exhibited, are possibly regulated by the apoptosis induction, scavenging of ROS and modulation of cellular signaling pathways to defy the cellular deafness during carcinogenesis. Despite the enriched bioactive compounds, the marine invertebrates are largely unexplored as identification, screening, pre-clinical and clinical assessment of lead compounds and their synthetic analogs remain a major task to be solved. In the current review, we focus on the principle strategy and underlying mechanisms deployed by the bioactive anticancer compounds derived from marine invertebrates to combat cancer with special insight into the cell death mechanism.

Antimicrobial lead compounds from marine plants

Marine environment is a home to a very wide diversity of flora and fauna, which includes an array of genetically diverse coastline and under seawater plant species, animal species, microbial species, their habitats, ecosystems, and supporting ecological processes. The Earth is home to an estimated 10 million species, of which a large chunk belongs to marine environment. Marine plants are a store house of a variety of antimicrobial compounds like classes of marine flavonoids—flavones and flavonols, terpenoids, alkaloids, peptides, carbohydrates, fatty acids, polyketides, polysaccharides, phenolic compounds, and steroids. Lot of research today is directed toward marine species, which have proved to be a potent source of structurally widely diverse and yet highly bioactive secondary metabolites. Varied species of phylum Porifera, algae including diatoms, Chlorophyta, Euglenophyta, Dinoflagellata, Chrysophyta, cyanobacteria, Rhodophyta, and Phaeophyta, bacteria, fungi, and weeds have been exploited by mankind for their inherent indigenous biological antimicrobial compounds, produced under the extreme stressful underwater conditions of temperature, atmospheric pressure, light, and nutrition. The present study aims at presenting a brief review of bioactive marine compounds possessing antimicrobial potency.

Calculation of the Global and Local Conceptual DFT Indices for the Prediction of the Chemical Reactivity Properties of Papuamides A-F Marine Drugs

A well-behaved model chemistry previously validated for the study of the chemical reactivity of peptides was considered for the calculation of the molecular properties and structures of the Papuamide family of marine peptides. A methodology based on Conceptual Density Functional Theory (CDFT) was chosen for the determination of the reactivity descriptors. The molecular active sites were associated with the active regions of the molecules related to the nucleophilic and electrophilic Parr functions. Finally, the drug-likenesses and the bioactivity scores for the Papuamide peptides were predicted through a homology methodology relating them with the calculated reactivity descriptors, while other properties such as the pKas were determined following a methodology developed by our group.

The Spirocyclic Imine from a Marine Benthic Dinoflagellate, Portimine, Is a Potent Anti-Human Immunodeficiency Virus Type 1 Therapeutic Lead Compound

In this study, we aimed to find chemicals from lower sea animals with defensive effects against human immunodeficiency virus type 1 (HIV-1). A library of marine natural products consisting of 80 compounds was screened for activity against HIV-1 infection using a luciferase-encoding HIV-1 vector. We identified five compounds that decreased luciferase activity in the vector-inoculated cells. In particular, portimine, isolated from the benthic dinoflagellate Vulcanodinium rugosum, exhibited significant anti-HIV-1 activity. Portimine inhibited viral infection with an 50% inhibitory concentration (IC₅₀) value of 4.1 nM and had no cytotoxic effect on the host cells at concentrations less than 200 nM. Portimine also inhibited vesicular stomatitis virus glycoprotein (VSV-G)-pseudotyped HIV-1 vector infection. This result suggested that portimine mainly targeted HIV-1 Gag or Pol protein. To analyse which replication steps portimine affects, luciferase sequences were amplified by semi-quantitative PCR in total DNA. This analysis revealed that portimine inhibits HIV-1 vector infection before or at the reverse transcription step. Portimine has also been shown to have a direct effect on reverse transcriptase using an in vitro reverse transcriptase assay. Portimine efficiently inhibited HIV-1 replication and is a potent lead compound for developing novel therapeutic drugs against HIV-1-induced diseases.

Marine sponges of the genus Stelletta as promising drug sources: chemical and biological aspects

Marine sponges of the genus Stelletta are well known as rich sources of diverse and complex biologically relevant natural products, including alkaloids, terpenoids, peptides, lipids, and steroids. Some of these metabolites, with novel structures and promising biological activities, have attracted a lot of attention from chemists seeking to perform their total synthesis in parallel to intensive biological studies towards new drug leads. In this review, we summarized the distribution of the chemically investigated Stelletta sponges, the isolation, synthesis and biological activities of their secondary metabolites, covering the literature from 1982 to early 2018.

Natural Cyclic Peptides as an Attractive Modality for Therapeutics: A Mini Review

Peptides are important biomolecules which facilitate the understanding of complex biological processes, which in turn could be serendipitous biological targets for future drugs. They are classified as a unique therapeutic niche and will play an important role as fascinating agents in the pharmaceutical landscape. Until now, more than 40 cyclic peptide drugs are currently in the market, and approximately one new cyclopeptide drug enters the market annually on average. Interestingly, the majority of clinically approved cyclic peptides are derived from natural sources, such as peptide antibiotics and human peptide hormones. In this report, the importance of cyclic peptides is discussed, and their role in drug discovery as interesting therapeutic biomolecules will be highlighted. Recently isolated naturally occurring cyclic peptides from microorganisms, sponges, and other sources with a wide range of pharmacological properties are reviewed herein.

Natural product-derived compounds in HIV suppression, remission, and eradication strategies

While combination antiretroviral therapy (cART) has successfully converted HIV to a chronic but manageable infection in many parts of the world, HIV continues to persist within latent cellular reservoirs, which can become reactivated at any time to produce infectious virus. New therapies are therefore needed not only for HIV suppression but also for containing or eliminating HIV reservoirs. Compounds derived from plant, marine, and other natural products have been found to combat HIV infection and/or target HIV reservoirs, and these discoveries have substantially guided current HIV therapy-based studies. Here we summarize the role of natural product-derived compounds in current HIV suppression, remission, and cure strategies.

Biotechnological Applications of Bioactive Peptides From Marine Sources

This review is an overview on marine bioactive peptides with promising activities for the development of alternative drugs to fight human pathologies. In particular, we focus on potentially prolific producers of peptides in microorganisms, including sponge-associated bacteria and marine photoautotrophs such as microalgae and cyanobacteria. Microorganisms are still poorly explored for drug discovery, even if they are highly metabolically plastic and potentially amenable to culturing. This offers the possibility of obtaining a continuous source of bioactive compounds to satisfy the challenging demands of pharmaceutical industries. This review targets peptides because of the variety of potent biological activities demonstrated by these molecules, including antiviral, antimicrobial, antifungal, antioxidant, anticoagulant, antihypertensive, anticancer, antidiabetic, antiobesity, and calcium-binding bioactivities. Several of these peptides have already gained recognition as effective drug agents in recent years. We also focus on cutting-edge omic approaches for the discovery of novel compounds for pharmacological applications. With rapid depletion of natural resources, omic technologies may be the solution to efficiently produce a vast variety of novel peptides with unique pharmacological potential.

Structural Diversity and Biological Activities of Cyclic Depsipeptides from Fungi

Cyclic depsipeptides (CDPs) are cyclopeptides in which amide groups are replaced by corresponding lactone bonds due to the presence of a hydroxylated carboxylic acid in the peptide structure. These peptides sometimes display additional chemical modifications, including unusual amino acid residues in their structures. This review highlights the occurrence, structures and biological activities of the fungal CDPs reported until October 2017. About 352 fungal CDPs belonging to the groups of cyclic tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, and tridecadepsipeptides have been isolated from fungi. These metabolites are mainly reported from the genera Acremonium, Alternaria, Aspergillus, Beauveria, Fusarium, Isaria, Metarhizium, Penicillium, and Rosellina. They are known to exhibit various biological activities such as cytotoxic, phytotoxic, antimicrobial, antiviral, anthelmintic, insecticidal, antimalarial, antitumoral and enzyme-inhibitory activities. Some CDPs (i.e., PF1022A, enniatins and destruxins) have been applied as pharmaceuticals and agrochemicals.

Structural Diversity and Biological Activities of Fungal Cyclic Peptides, Excluding Cyclodipeptides

Cyclic peptides are cyclic compounds formed mainly by the amide bonds between either proteinogenic or non-proteinogenic amino acids. This review highlights the occurrence, structures and biological activities of fungal cyclic peptides (excluding cyclodipeptides, and peptides containing ester bonds in the core ring) reported until August 2017. About 293 cyclic peptides belonging to the groups of cyclic tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, undeca-, dodeca-, tetradeca-, and octadecapeptides as well as cyclic peptides containing ether bonds in the core ring have been isolated from fungi. They were mainly isolated from the genera Aspergillus, Penicillium, Fusarium, Acremonium and Amanita. Some of them were screened to have antimicrobial, antiviral, cytotoxic, phytotoxic, insecticidal, nematicidal, immunosuppressive and enzyme-inhibitory activities to show their potential applications. Some fungal cyclic peptides such as the echinocandins, pneumocandins and cyclosporin A have been developed as pharmaceuticals.

Structural diversity of marine cyclic peptides and their molecular mechanisms for anticancer, antibacterial, antifungal, and other clinical applications

Many cyclic peptides and analogues derived from marine sources are known to possess biological properties, including anticancer, antitumor, antibacterial, antifungal, antiparasitic, anti-inflammation, anti-proliferative, anti-hypertensive, cytotoxic, and antibiotic properties. These compounds demonstrate different activities and modes of action according to their structure such as cyclic oligopeptide, cyclic lipopeptide, cyclic glycopeptide and cyclic depsipeptide. The recent advances in application of the above-mentioned cyclic peptides were reported in dolastatins, soblidotin, didemnin B, aplidine, salinosporamide A, kahalalide F and bryostatin 1 and they are currently in clinical trials. These cyclic peptides are possible novel drugs discovered and developed from marine origin. Literature data concerning the potential properties of marine cyclic peptides were reviewed here, and the structural diversity and biological activities of marine cyclic peptides are discussed in relation to the molecular mechanisms of these marine cyclic peptides.

Anticancer potential of bioactive peptides from animal sources (Review)

Cancer is the most common cause of human death worldwide. Conventional anticancer therapies, including chemotherapy and radiation, are associated with severe side effects and toxicities as well as low specificity. Peptides are rapidly being developed as potential anticancer agents that specifically target cancer cells and are less toxic to normal tissues, thus making them a better alternative for the prevention and management of cancer. Recent research has focused on anticancer peptides from natural animal sources, such as terrestrial mammals, marine animals, amphibians, and animal venoms. However, the mode of action by which bioactive peptides inhibit the proliferation of cancer cells remains unclear. In this review, we present the animal sources from which bioactive peptides with anticancer activity are derived and discuss multiple proposed mechanisms by which these peptides exert cytotoxic effects against cancer cells.

Peptides, Peptidomimetics, and Polypeptides from Marine Sources: A Wealth of Natural Sources for Pharmaceutical Applications

Nature provides a variety of peptides that are expressed in most living species. Evolutionary pressure and natural selection have created and optimized these peptides to bind to receptors with high affinity. Hence, natural resources provide an abundant chemical space to be explored in peptide-based drug discovery. Marine peptides can be extracted by simple solvent extraction techniques. The advancement of analytical techniques has made it possible to obtain pure peptides from natural resources. Extracted peptides have been evaluated as possible therapeutic agents for a wide range of diseases, including antibacterial, antifungal, antidiabetic and anticancer activity as well as cardiovascular and neurotoxin activity. Although marine resources provide thousands of possible peptides, only a few peptides derived from marine sources have reached the pharmaceutical market. This review focuses on some of the peptides derived from marine sources in the past ten years and gives a brief review of those that are currently in clinical trials or on the market.

Antiproliferative and Proapoptotic Activities of Marine Sponge Hyrtios erectus Extract on Breast Carcinoma Cell Line (MCF-7)

Background:

Marine sponge is a rich natural resource of many pharmacologically important compounds.

Objective:

Marine sponge Hyrtios erectus, collected from North Bay, South Andaman Sea, India, was screened for potential antiproliferative and proapoptotic properties on a breast adenocarcinoma cell line (MCF-7).

Materials and Methods:

3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to test the antiproliferative and cytotoxicity effects of the sponge extract. Analysis of apoptosis and cell cycle stages were done by flow cytometry. The expression of several apoptotic-related proteins in MCF-7 cells treated by the extract was evaluated by Western blot analysis. Various analytical techniques including Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, and nuclear magnetic resonance were employed to determine the identity of the active compounds in the sponge extract.

Results:

N-Hexane extract of the sponge inhibited proliferation of the MCF-7 cell line in a dose- and time-dependent manner. Exposure of the sponge extract triggered apoptosis of the MCF-7 cells, induced DNA fragmentation, and arrested the cells in G₂/M phase. Treatment of the sponge extract induced downregulation of antiapoptotic Bcl-2 protein and upregulation of Bax, caspase-3, caspase-9, and fragmented poly(ADP ribose)polymerase proteins in MCF-7 cells. Five bioactive compounds have been identified in the extract.

Conclusion:

The antiproliferative and proapoptotic activities of the tested extract suggested the pharmacologic potential of the identified compounds. Further characterization of the identified compounds are in progress.

SUMMARY

The N-hexane extract of the marine sponge Hyrtios erectus, collected from North Bay, South Andaman Sea, India, showed potential antiproliferative and proapoptotic properties against a breast adenocarcinoma cell line (MCF-7).

The sponge extract retarded the growth of breast carcinoma cell line MCF-7 cells in a time- and dose-dependent manner.

The sponge extract induced apoptosis of breast cancer cell line MCF-7 and arrested cells in G₂/M phase.

The sponge extract induced downregulation of Bcl-2 protein in MCF-7 cell line and upregulation of Bax, caspase-3, and cleaved PARP. Five bioactive compounds have been identified in the extract.

Abbreviations used: GC-MS: Gas chromatography-mass spectrometry; FT-IR: Fourier transform infrared spectroscopy; NMR: Nuclear magnetic resonance; MTT: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide.

Phakellistatins: An Underwater Unsolved Puzzle

A critical summary on the discovery of the nineteen members of the phakellistatin family (phakellistatin 1–19), cytotoxic proline-rich cyclopeptides of marine origin, is reported. Isolation, structural elucidation, and biological properties of the various-sized natural macrocycles are described, along with the total syntheses and the enigmatic issues of the cytotoxic activity reproducibility.

Cytotoxic Compounds Derived from Marine Sponges. A Review (2010-2012)

Abstract: This extensive review covers research published between 2010 and 2012 regarding new compounds derived from marine sponges, including 62 species from 60 genera belonging to 33 families and 13 orders of the Demospongia class (Porifera). The emphasis is on the cytotoxic activity that bioactive metabolites from sponges may have on cancer cell lines. At least 197 novel chemical structures from 337 compounds isolated have been found to support this work. Details on the source and taxonomy of the sponges, their geographical occurrence, and a range of chemical structures are presented. The compounds discovered from the reviewed marine sponges fall into mainly four chemical classes: terpenoids (41.9%), alkaloids (26.2%), macrolides (8.9%) and peptides (6.3%) which, along with polyketides, sterols, and others show a range of biological activities. The key sponge orders studied in the reviewed research were Dictyoceratida, Haplosclerida, Tetractinellida, Poecilosclerida, and Agelasida. Petrosia, Haliclona (Haplosclerida), Rhabdastrella (Tetractinellida), Coscinoderma and Hyppospongia (Dictyioceratida), were found to be the most promising genera because of their capacity for producing new bioactive compounds. Several of the new compounds and their synthetic analogues have shown in vitro cytotoxic and pro-apoptotic activities against various tumor/cancer cell lines, and some of them will undergo further in vivo evaluation.

First Total Synthesis and Biological Screening of a Proline-Rich Cyclopeptide from a Caribbean Marine Sponge

A natural heptacyclopeptide, stylissamide G (7), previously isolated from the Bahamian marine sponge Stylissa caribica from the Caribbean Sea, was synthesized via coupling of the tetrapeptide l-phenylalanyl-l-prolyl-l-phenylalanyl-l-proline methyl ester with the tripeptide Boc-l-leucyl-l-isoleucyl-l-proline, followed by cyclization of the linear heptapeptide fragment. The structure of the synthesized cyclooligopeptide was confirmed using quantitative elemental analysis, FT-IR, ¹H NMR, ¹³C NMR and mass spectrometry. Results of pharmacological activity studies indicated that the newly synthesized cycloheptapeptide displayed good anthelmintic potential against Megascoplex konkanensis, Pontoscotex corethruses and Eudrilus eugeniea at 2 mg/mL and in addition, potent antifungal activity against pathogenic Candida albicans and dermatophytes Trichophyton mentagrophytes and Microsporum audouinii at a concentration of 6 μg/mL.

Alkynyl-Containing Peptides of Marine Origin: A Review

Since the 1990s, a number of terminal alkynyl residue-containing cyclic/acyclic peptides have been identified from marine organisms, especially cyanobacteria and marine mollusks. This review has presented 66 peptides, which covers over 90% marine peptides with terminal alkynyl fatty acyl units. In fact, more than 90% of these peptides described in the literature are of cyanobacterial origin. Interestingly, all the linear peptides featured with terminal alkyne were solely discovered from marine cyanobacteria. The objective of this article is to provide an overview on the types, structural characterization of these unusual terminal alkynyl fatty acyl units, as well as the sources and biological functions of their composed peptides. Many of these peptides have a variety of biological activities, including antitumor, antibacterial, antimalarial, etc. Further, we have also discussed the evident biosynthetic origin responsible for formation of terminal alkynes of natural PKS (polyketide synthase)/NRPS (nonribosome peptide synthetase) hybrids.